1. Field of the Invention
The present invention relates to a structure and a jig for mounting a least a spring arm on at least a head arm, or more in particular to a structure for mounting spring arms on corresponding head arms and a mounting jig for assuring a structure free of resonance between each head arm and the corresponding spring arm.
2. Description of the Related Art
A disk apparatus for recording information on a discoidal medium (disk) using a head or reading the information recorded in the disk through the head has come to find application as an external storage unit for a computer system. Such a disk apparatus includes a magnetic disk apparatus for recording information using magnetism and an optical disk apparatus for recording information using light. Generally, a disk apparatus exchanges information with a disk by way of a head mounted at the forward end of a head actuator of a swinging type.
The recording density of such a disk apparatus as a magnetic disk apparatus is increasing and the cost thereof is being constantly reduced. As for the head actuator it is crucial to improve the positioning accuracy with which the head is located on the track of the disk on the one hand and to reduce the manufacturing cost on the other. Especially, a large-capacity magnetic disk apparatus with a track pitch of less than 3 .mu.m has recently been developed. In such an apparatus, the data recording and reproducing operations are adversely affected by a positioning error of 1 .mu.m or less of the head actuator.
If the head arm (also called the carriage) constituting the head actuator shares a resonance point with the corresponding spring arm (also called the load beam) mounted at the forward end of the head arm, the vibration would be exaggerated and deteriorate the head positioning accuracy. Therefore, each head arm and each spring arm are generally designed with the resonance points thereof displaced from each other.
In the event that the connection between a head arm and a corresponding spring arm is not sufficient or in the event that only inappropriate portions thereof are coupled, however, the system for supporting the spring arm is varied, with the frequent result that the resonant point of the system is displaced to such an extent as to cause unnecessary vibrations. Development of a preventive measure against this inconvenience has been desired.
FIGS. 1A to 1C show an example of a structure for mounting spring arms 3 on corresponding head arms 1, respectively, of a head actuator 10 of a conventional disk apparatus such as a magnetic disk apparatus. In this head actuator 10, as shown in FIG. 1B, four head arms 1 are integrally formed with a rotor 1R, into the E-shape as viewed sideways, by aluminum die-casting. Each spring arm 3 is mounted at the forward end of the corresponding head arm 1 through a fixing member 2, and a head 4 is mounted at the forward end of the spring arm 3.
The forward end of the head arm 1 is formed with a caulking hole 6, as shown in FIG. 1C, and the base of the fixing member 2 is formed with a cylindrical protrusion 21 adapted to fit into the caulking hole 6. The base of the spring arm 3 is mounted by spot welding to the fixing member 2, which in turn is fixed on the head arm 1 by caulking (press fitting) with the protrusion 21 thereof inserted in the caulking hole 6. Also, the head 4 is fixedly mounted by bonding at the forward end of the spring arm 3.
The surface of each head arm 1 facing the fixing member 2 is machined to an accuracy of not more than several tens of a .mu.m in error with reference to the bearing contact surface B of the rotor 1R beforehand. In mounting the fixing member 2 on each head arm 1 by caulking, therefore, as shown by character A in FIG. 1C, the fixing member 2 is kept in close contact with the machined surface of the head arm 1 so that a desired mounting height accuracy of the head 4 may be obtained with reference to the bearing contact surface B shown in FIG. 1B.
In the large-capacity magnetic disk apparatuses recently developed, the requirement of an increased number of disks and a reduced air-bearing height of the magnetic head makes it necessary to strictly secure the mounting accuracy of the magnetic heads and the head arms in the air-bearing direction of the heads. In the conventional method of securing a mounting accuracy in the air-bearing direction of the head, the portion of the head arm 1 where the spring arm 3 is mounted is machined with high accuracy, and the surface of the fixing member 2 is kept in close contact with the high-accuracy machined surface portion of the head arm 1 to determine the height of the magnetic head.
In the conventional structure for mounting at least a spring arm 3 on at least a head arm 1, however, it is necessary to machine with high accuracy as many contact surfaces of the fixing members 2 at the forward ends of the head arms 1 as there are heads 4 to be mounted. Also, in the case where a sufficient thickness cannot be secured for the head arm 1, it is difficult to secure the required accuracy after machining, thereby leading to the problems of an increased machining cost and a lower machining yield.
Further, even in the case where the head arms 1 are produced by inexpensive means such as by plate punching or by integral molding with the rotor 1R by resin molding or aluminum die-casting, the requirement of high-accuracy machining of the forward ends of the head arms 1 constitutes a stumbling block to a cost reduction of the head actuator 10.
Furthermore, in securing the high-accuracy machined surfaces of the head arms 1 to the corresponding fixing members 2 by caulking, respectively, it is a common practice to insert a comb-shaped pressure member in the comb gaps of the head arms 1 to bring the head arms 1 into close contact with the corresponding fixing members, respectively. The variations in the machining dimensions from one head arm 1 to another, however, makes it difficult to bring all the fixing members 2 into close contact with the corresponding head arms 1 in exactly the same manner. As a result, one head arm 1 may be in close contact with the corresponding fixing member 2 in a manner different from the manner in which another head arm 1 is in close contact with the corresponding fixing arm 2. This contact variation causes varied vibration characteristics of the head units and adversely affects the head positioning accuracy.
Specifically, one of the primary causes of a vibration generated in the magnetic head during the recording or reproducing operation is derived from the phenomenon (coupled vibration) in which the vibration of the assembly of the head 4 and the spring arm 3 supporting the head 4 is undesirably coupled with the vibration of the head arm 1 in the case where the natural frequency of the assembly is comparatively close to the natural frequency of the head arm 1. Normally, the assembly and the head arm 1 are designed to have natural frequencies that will not cause any coupled vibration. In the case where the head arm 1 and the corresponding spring arm 3 are coupled to each other by such means as caulking or a screw, however, the head arm 1 and the spring arm 3 are not always kept in close contact with each other over the entire surfaces thereof, but the apparent natural frequency of the spring arm 3 changes with the degree to which it is in contact with the head arm 1, thereby causing a coupled vibration with the head arm 1.